The present invention relates to an apparatus for blocking a medium flow passage in a spray head. The apparatus comprises a blocking element, such as a burst disk, arranged in the passage. When unbroken, the blocking element blocks the passage of medium flow from a first side of the blocking element to a second side of the blocking element. On the first side of the blocking element a first pressure prevails in the passage, while on the second side of the blocking element a second pressure prevails in the passage. The blocking element has been arranged to be ruptured so as to form a passage for the medium through the blocking element when the pressure difference between the first and the second sides of the blocking element reaches a preset value.
In fire extinguishing technology, solutions are also known in which the flow passage of an extinguishing medium is provided with an element rupturable by the prevailing pressure (burst disk, rupture disk), placed between a liquid source and a spraying nozzle to block the passage. These are ruptured when the pressure difference in the passage on different sides of the burst disk exceeds a given value, which is characteristic to each burst disk. A solution of this type is described e.g. in the publication Fire Protection Handbook, 18th Edition, 1997, pages 6-200. Specification DE 19948324 discloses a corresponding solution. In prior-art solutions, the burst disk is so designed that it is bound to be ruptured when the pressure difference increases sufficiently. Therefore, incidental pressure variations occurring in the piping e.g. due to a malfunction may cause a rupture of the burst disk, which again results in significant extra costs. If the burst disk is so designed that it will not be ruptured until the pressure difference has reached a very high value, this may jeopardize reliable operation of the system in a fire situation. Solutions have therefore been developed in which the burst disk is ruptured by using separate devices to pierce the burst disk. These have not always been satisfactory in operation or they have been complicated and required energy from outside in order to work.
On the other hand, prior-art devices known in fire extinguishing technology include sprinkler heads provided with a valve element which in a non-activated state blocks the liquid flow passage and, when the sprinkler is activated upon being triggered, e.g. when a heat activated ampoule is broken, moves into a position where the extinguishing medium can flow into one or more nozzles. These solutions use dynamic seals, such as 0-rings, to seal the space between the valve element and the flow passage wall In the non-activated state. A sprinkler head of this type, which uses ring-like seals, is disclosed in U.S. Pat. No. 5,967,239 (Sprakel, et al.). In recent times there has appeared a need to avoid the use of dynamic seals in spray heads used for fire extinguishing purposes. In addition, the clearances between the valve element or shaft and the sprinkler body typically have to be made very small.
The object of the present invention is to achieve a completely new type of solution in conjunction with blocking elements to ensure their reliable operation. On the other hand, a second object is to achieve a compact solution in conjunction with spray heads to avoid the use of dynamic seals.